1. Lesson Objectives
To understand how to add 4 and 8 bit binary numbers together
To understand what is meant by the term “Overflow”
ALL students will add 4 bit binary numbers successfully
MOST students will add 8 bit binary numbers successfully
SOME students will be able to discuss why overflow errors occur

2. + Adding Denary Numbers 1 2 5 4 6 3
What are the steps that we do to add 2 denary numbers together? 1 2 5 4 6 3 + 2 8 1 7 1
Carryover

3. + Adding Binary numbers 1 We do it in exactly the same way 1 1 1 1
1+1 = 2
In binary this is 10
We do it in exactly the same way
0+1 = 1
1+0 = 1 1 + 1 1 1 1
Carryover
0+0+1=1

4. Always convert it back to denary to check the answer 1 5+ 6 11 + 1 1 1 1
Carryover

5. Task 1: Have a go at the additions in your book.
Remember that in binary
0+0=0
1+0=1
0+1=1
1+1=2=10
When carrying over
1+1+1 = 3 = 11

6. Overflow Errors Sometimes we run into problems.
Suppose we have eight bits in each location.
When we add the binary equivalent of denary :
There is no room for a carry so it is lost and we get the wrong answer, 39 instead of 295.
When there isn’t enough room for a result, this is called overflow and produces an overflow error.
Denary
Binary
150 1
+145
= 39
(1)
Carry
Remember the maximum 8 bit binary number 255

7. On the front of your booklets
Write down the definitions for Overflow Error

8. How did you do? A/A* - 8/8 8 bit correct B – 6/7 8 bit correct
C – 4/5 8 bit correct
D - 6/6 4 bit numbers

9. Plenary

10. In pairs
Count up the binary numbers using your fingers to represent the digits.
Test each other –